Crossrail employees walk in the new Farringdon underground station of the Elizabeth line which was due to open in December 2018, in London.
Photograph: Peter Nicholls/Reuters

The opening of the £15bn Crossrail line across London will be delayed by up to a year, it has been announced, after months of rumours that the engineering scheme was facing increasing difficulties.

The train line, which has been decades in the planning and will link west and east London with faster, high-capacity services, was due to open in December. But Crossrail executives admitted it would not be ready for its planned official opening as the Elizabeth line by the Queen, after a series of problems and delays.

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It said the central section of the line, travelling under the capital from Paddington to Abbey Wood, would now not open until autumn 2019 to complete building work and allow for extensive testing to ensure it opened as a safe and reliable railway.

The delay will disappoint thousands of commuters but could also spell more trouble for cash-strapped Transport for London, which faces a near-£1bn deficit. Forecast revenues from Crossrail play a significant part in its business plan and to mayor Sadiq Khan’s fare freeze, which will come under further scrutiny.

Critics accused the government of smuggling out bad news before the return of parliament and questioned why Crossrail executives had been rewarded with new jobs.

Andrew Adonis, the former chair of the national infrastructure commission, said: “It’s clearly a further massive catastrophe for Chris Grayling, who didn’t say a word in public about the scale of the crisis. He himself moved Sir Terry Morgan to be chair of HS2 and that was soon after Andrew Wolstenholme, the chief executive, left.

“The biggest infrastructure project in Europe, in a state of crisis, lost both its leaders with Grayling being awol throughout. To me it’s utterly inexplicable. How can it give anyone confidence that HS2 will be delivered?”

Lord Adonis said the full scale of the problems had yet to emerge, with the industry talking of major issues with signalling systems, and predicted the opening could now be delayed until 2020.

Crossrail bosses, paid some of the largest salaries in the public sector, had long boasted that the complex project was being delivered on time and on budget, but this summer the government and TfL were forced to increase the £14.8bn budget by another £650m. Design, construction and engineering has lasted 10 years with different infrastructure contracts, new trains and three signalling systems.

The Crossrail chief executive, Simon Wright, said: “The Elizabeth line is one of the most complex and challenging infrastructure projects ever undertaken in the UK and is now in its final stages. We have made huge progress with the delivery of this incredible project but we need further time to complete the testing of the new railway.

“We are working around the clock with our supply chain and Transport for London to complete and commission the Elizabeth line.”

Elizabeth line trains are operating already overground between Shenfield and Liverpool Street and between Paddington and Hayes and Harlington. Crossrail said construction activity was drawing to a close: an assessment in June said the project was 93% complete.

An electrical explosion in east London this year exacerbated construction problems and caused further delays, but Crossrail had maintained until that the December opening remained possible.

The Elizabeth line should eventually boost the space for passengers to travel through central London by 10%. The line will link the West End with Heathrow and Canary Wharf and serve suburbs in the east and west, and more than 200 million passengers are expected to use it every year.

London politicians called for an inquiry. The Conservative assembly member Keith Prince said the mayor had no contingency plan, despite warnings. He said: “Sadiq Khan’s financial plans were hugely reliant on Crossrail opening on time, on budget and meeting incredibly optimistic passenger targets.”

Unions were equivocal, with jobs now extending on Crossrail for another year, However, the TSSA general secretary, Manuel Cortes, admitted it was “hard to see the mayor will be able to make ends meet” and called for the Commons and assembly’s transport committees to hold hearings.

A spokesperson for the mayor said it was disappointing but that Crossrail was “one of the most complex engineering schemes ever undertaken”. He added: “It is essential that a safe and reliable railway operates from day one, and this has to be the top priority.”

Retailers expressed concern about the delay. Jace Tyrrell, the chief executive of New West End Company, said: “The economic benefits expected from the Elizabeth line were a welcome boost for West End retailers. The postponement makes it even more imperative that government acts now to support the nation’s high street businesses.”